Tar reduction by inorganic halide for reaction of unsaturated anhydride and polybutene

ABSTRACT

Viscous polybutenes of number average molecular weight (M n ) in the range of about 300 to about 3,000 have improved reactivity with intramolecular anhydrides of unsaturated aliphatic dicarboxylic acids when reacted in the presence of rather small amounts, i.e., 5 to 200 ppm, of inorganic halogen preferably chlorine and/or bromine containing compounds. Use of such halogen containing compounds in the addition reaction of polybutene with said unsaturated anhydrides can reduce formation of undesired tarry product resulting from polymerization and/or thermal decomposition of the unsaturated anhydrides.

BACKGROUND OF INVENTION

Viscous polybutenes of about 300 to about 3,000 M_(n) have viscositiesin the range of about 4 to about 5,500 centistokes at 100°C. Suchpolybutenes are commercially available from polymerization of refinerybutenes; isobutylene, cis-butene-2and butene-1 generally present withbutane in a C₄ fraction. Commercially since about 1940, such C₄fractions with or without added isobutylene, or isobutylene richconcentrates has been polymerized in the presence of Friedel-Craftscatalyst. The wide range in viscosity and molecular weight depends, asis known, on polymerization temperature, to a lesser extent on catalystand its concentration, and on the olefin content of the feed. Theviscous polybutenes are essentially water white and thermally decomposewith no residue at temperatures above 275°C. and have some useapplications in engine oils as anti-scuff agents and viscosity indeximprovers and in fuels for internal combustion engines to reduce orsuppress deposits in the fuel induction system.

The viscous polybutenes have also found use as components of caulkingcompounds, adhesives and electric-cable insulating oils. However, thegreatest use of the viscous polybutenes is as a raw material in themanufacture of addition agents for fuels and gasoline because theviscous polybutenes are reactive olefins and provide branched-chainalkyl structure in derivatives enhancing their solubility in petroleumproducts such as lubricant oils, fuels and refinery streams. Thederivatives of most interest in the past 15 years are from thepolybutenyl-substituted intramolecular anhydrides of aliphaticdicarboxylic acids such as succinic anhydride. Thepolybutenylsubstituted saturated aliphatic anhydrides have been used perse, or as diesters, amides, imides, amidines, imidines, and neutral oroverbased basic metal salts as addition agents in petroleum products.The addition agents from polybutenes of M_(n) below 500 are mainly usedin fuels; for example in gasoline to inhibit rusting, carburetordeposits, and carburetor icing and in diesel fuels to inhibit rust,corrosion and smoke, and in motor oils and industrial oils as rust andwear inhibitors.

The addition agents from polybutenes of 500 to about 3,000 M_(n) havefound extensive use as detergent-dispersants in motor oils and lesseruse as carburetor detergents in gasoline, heat exchanger antifoulants inrefinery streams, rust and corrosion inhibitors in surface coatings andas emulsifiers and demulsifiers.

The viscous polybutenes are complex mixtures of polymers, copolymers andinterpolymers of isobutylene, cis-butene-2 and butene-1. The nature andrelative amounts of the butene monomers involved in the polymerizationleading to a particular M_(n) polybutene are not indicative of theresulting polymer product because extensive isomerization occurs duringpolymerization. The viscous polybutenes, although largely mono-olefins,may contain 0 to 20% isoparaffins. The unsaturation in the viscouspolybutene molecules is predominantly in a terminal or near terminalgroup which, as later illustrated, are of the trisubstituted orvinylidene type. The non-olefinic chain portion of the polybutenemolecules is composed of normal butyl and isobutyl monomer units andhence is a long and branched alkyl chain. Such long, branched alkylchain of the lighter (below 500 M_(n)) polybutenes contain relativelygreater amounts of normal butyl units and lesser amounts of isobutylunits. The heavier (500-3,000 M_(n)) polybutenes contain relativelygreater amounts of isobutyl units and lesser amounts of normal butylunits which are concentrated near the end of the long, branched alkylchain. For example, the structures of a polydisperse polybutene of about900 M_(n) have in-part been identified through the use of infraredspectroscopy (calibrated by NMR) and permanganate cleavage. Theprincipal structures identified are shown below (in decreasing order ofconcentration): ##EQU1## wherein R is the long, branched alkyl chain andcomprises about 60 mole % (C₄)₄ to ₃₅, about 30 mole % (C₄)₁₂ to ₃₅ andabout 10 mole % (C₄) > ₃₅ ; R' is mainly methyl but is also ethyl; andthe ratio of iso-C₄ to n-C₄ is about 3:1.

With respect to polybutene addition reactivity with unsaturatedintramolecular anhydrides, it is believed, that the olefinic terminalgroups in the three structures shown above are in the decreasingreactivity order of III, I and II. In the uncatalyzed addition reaction,some of the slower reacting molecular species remain unreacted and withthe isoparaffinic polymer species (0-20% of the total polymer product)which do not react at all, the desired polybutenyl-substituted saturatedanhydride product can be obtained in yields of 75-80% based on startingpolymer.

Such addition reaction between the viscous polybutene and intramolecularanhydride of unsaturated aliphatic dicarboxylic acid can typically useany one of maleic anhydride, citraconic anhydride, itaconic anhydride,ethyl maleic anhydride, halo (e.g., chloro-) maleic anhydride,glutaconic anhydride, homomesaconic anhydride, and the like according toU.S. Pat. Nos. 2,628,942 and 2,634,256 among others. The additionreactions are, in general, conducted at temperatures in the range of150° to 300°C using polybutene to anhydride molar ratios of reactants inthe range of 1.0:1.0-15, generally 1.0:1.05-1.15. In addition to thenon-reaction of some olefinic species of polybutene and isoparaffinicentities thereof amounting to a total of up to 40-50% of the polybutenecharged, there is also a problem with respect to thermal decompositionand polymerization of the unsaturated anhydride reactant at temperaturesupward from 150°C.

Thermal decomposition at temperatures upward from 150°C of unsaturatedaliphatic dicarboxylic acids and their anhydrides (e.g. maleic and itsanhydride) has been known and is reported, for example in U.S. Pat. No.3,476,774 which gives earlier documentation sources therefor. Suchthermal decomposition is accompanied by evolution of water vapor andoxides of carbon, in a closed reaction vessel, is accompanied by anincrease in internal pressure. Under some observed conditions thethermal decomposition can be so substantially instantaneous as to beexplosive. In the absence of explosive thermal decomposition acarbon-containing residue is also formed in addition to water vapor andoxides of carbon. Such thermal decomposition and attendantpolymerization of the unsaturated anhydride reactant has been observedas occurring during its addition reaction with polymeric olefins, e.g.polybutenes and others, in a closed reaction vessel. There is theincrease of internal pressure by involved water vapor and oxides ofcarbon (mainly CO₂) but the attendant carbon-containing residue variesin nature from somewhat granular when the decomposition is only slightto a tarry material mainly adhering to internal surfaces of the reactionvessel when the decomposition is more extensive but well below explosivemagnitude. The granular type residue amounts to from about 0.1 to about0.3 weight percent of the total charge, in general, is dispersed in theproduct, the alkenylsubstituted saturated anhydride addition compounddiluted with unreacted components of the olefin polymer, is readilyseparated therefrom by filtration. However, the tarry residual product,which for the most part fouls the internals of the reaction vessel canbe as high as 2-3 weight percent of the total charge. The tarry residualmaterial not adhering to reactor internals fouls the filter andinterferes with filtration of the desired reaction product. Both typesof residue are undesirable because of the above noted foulingcharacteristics and because their formation results in yield reductionof the desired alkenyl-substituted anhydride addition product.

Various means have been proposed and/or used to suppress thermalconversion of unsaturated anhydride reactant. German Pat. No. 1,102,142for its reaction of triene (e.g., 1,5,9-cyclododecatriene) with maleicanhydride to prepare a 1:1 addition product teaches the use of from 0.01to 5 weight percent of thionine, phenothiazine, hydroquinone, andrelated inhibitors. U.S. Pat. No. 3,231,587 teaches the use of chlorinegas in molar amounts equal to maleic anhydride for its addition reactionwith olefin polymers (the resulting alkenylsuccinic anhydride contains0.4-0.5 weight percent chlorine) as a superior to earlier proposed firstpreparing a chlorinated olefinic polymer 4-15 weight percent chlorineand reacting the chloro-polymer with maleic anhydride. U.S. Pat. No.3,476,774 teaches the use of a hindered phenol non-reactive with theolefin polymer or maleic anhydride (e.g. 2,6-di-tertbutylphenol or4,4'-methylenebis-2,6-ditert-butylphenol) to suppress thermaldecomposition.

Such hindered phenols are not readily removed from the adduct product.The chloro-substituted adduct may not be useful in all cases for thepreparation of addition agent derivatives.

In our laboratories the use of small, i.e., catalytic amounts ofhydrogen chloride during the adduct formation between olefinic polymerand maleic anhydride achieved success in improving yield and reducingformation of undesired tarry material. A drawback of this method is thepossible corrosive nature of the stored product. However, it isunderstood, that hydrogen halides can react with the olefinic polymerforming alkyl halides. It is also recognized, that at highertemperatures, due to decomposition of the alkyl halides, hydrogen halideand halogen formation are possible. Hence it is recognized, thataddition of trace quantities of hydrogen halide or halogen or alkylhalide to the polymer could achieve the desired improvements in theaddition reaction. It was also recognized, that the effectiveness ofsaid halocompounds will vary with process conditions and exact chemicalnature and concentration of the added material.

From the standpoint of both the manufacturer-merchant of the viscouspolybutenes and the purchasers-users thereof it would be desirable tomodify such polybutene compositions by addition of a small amount ofmaterial which enhances reactivity of the polybutene and suppressesformation of the undesirable tarry material without undesirable addedeffects. It would be further desirable that such modification of thepolybutenes be accomplished by a simple, single process step of not onlycombining a small amount of material with the polybutene to effect thedesired reactivity enhancement and tarry material suppression but alsoby use of a material which is readily removable from the adduct reactionproduct. For this latter benefit it is pointed out that unreactedanhydride, including that used in slight molar excess per mole ofpolybutene, is removed from the adduct reaction product by evaporationat an absolute pressure in the range of 5 to 760 mm Hg. and at atemperature below reaction temperature. Thus it is beneficial to add tothe polybutene such materials having the above-beneficial effects on theadduct reaction and at the same time readily removable at saidtemperature and pressure conditions at which unreacted unsaturatedanhydride is removed or merely by filtration.

SUMMARY OF INVENTION

It has now been discovered that viscous polybutenes of from about 300 toabout 3,000 M_(n) containing 10 to 200, preferably from 5 to 200 ppm onweight basis of halogen, more suitably chlorine and/or bromine,containing inorganic compound provides a novel, uniquely modifiedreaction between the unsaturated anhydride and polybutene attemperatures of 150°-300°C without affecting chemical substitution ofeither the reactants or the adduct product. The inorganichalogen-containing additive can be removed from the adduct product underconditions of removing unreacted unsaturated-anhydride and its useenhances polybutene conversion to adduct, and suppresses tarry materialformation.

To be most readily removable with unreacted unsaturated anhydride at 5to 760 mm Hg., the inorganic halide additive or its decompositionproduct should have sufficient vapor pressure at such pressures tofacilitate their removal or should be removable by solid-liquidseparation, e.g. filtration or centrifugation.

Typical, but not all inclusive, of such chlorine and/orbromine-containing inorganic halides are dry hydrogen chloride orbromide, iodine, iodine monochloride or monobromide and calcium bromide.

The reaction between the viscous polybutenes and the anhydrides ofunsaturated aliphatic dicarboxylic acids known to the art to be usefulfor the addition reaction producing alkenyl-substituted saturatedanhydride, is conducted commercially is a batchwise or continuous mannerin a stirred-tank type autoclave or equivalent reaction vessel providingintimate contact between the reactants. For batchwise operation thereactants are charged to the closed reaction vessel with or withoutdisplacing its air with oxygen-free, e.g. nitrogen, atmosphere atambient pressure. The reactants can be at ambient temperature but thepolybutene reactant is usually at an elevated temperature to reduce thetime for the reaction mixture to reach reaction temperature. Solidanhydride reactant can be charged alone or dispersed in polybutene oralone as a melt. The reaction mixture is stirred while being heated toreaction temperature and during reaction.

Continuous conduct of the addition reaction is maintained by charging tothe reaction vessel containing the stirred adduct forming reactionmixture a melt of the anhydride reactant and preheated viscouspolybutene so that their combined heat supplies the heat input neededduring reaction.

Reaction time for batchwise operation is, in general, 4-8 hours.Continuous operation requires, in general, a shorter residence time, forexample 1-3 hours.

Thermal decomposition of anhydride reactant, which evolves CO₂ and watervapor, causes an undesirable pressure increase as well as formation ofundesirable tarry material during the adduct reaction. Such pressureincrease, although undesirable, can be used as an indicator of failureto suppress formation of such tarry material by the additive of thepolybutene composition. The actual extent of formation of such tarrymaterial is, of course, determined gravimetrically after termination ofthe addition reaction and removal of unreacted anhydride reactant at thebefore mentioned pressure in the range of 5 to 760 mm Hg.

The manner and nature of enhanced adduct yield of the inorganic halideis not understood. We speculate that isomerization of the olefin doublebond to a more reactive species is accomplished under the effect oftrace decomposition products derived from the inorganic halide. Further,such trace impurities can also act as radical quenchers and inhibit thedecomposition or polymerization of unsaturated anhydride to tar.

The use of the present inventive halogen-containing additives and thebenefits to be derived therefrom in addition reactions with the beforementioned unsaturated anhydride will now be illustrated using maleicanhydride, most commonly, commercially used of those anhydridereactants. In the examples the amount of polybutene to maleic anhydrideused was in molar ratio of 1.0:1.1.

In the first five examples the polybutene having 914 M_(n) with 14 ppmchloride (from polymerization catalyst) was used in a 22 ml volume Parrbomb having a magnetic stirrer. In each illustrative example 10.0 gramsof polybutene and about 1.1 grams of powdered maleic anhydride (MA) toprovide a polymer: MA mole ratio of 1.0:1.1 are charged at ambienttemperature to the bomb. Air is displaced from the bomb with nitrogengas, the bomb is sealed, the sealed bomb immersed in a 254°C oil bath,the reaction mixture is stirred for six hours, and then sampled. Aweight aliquot portion of each reaction product so produced ischromatographed on silica gel column. The unreacted polybutene is elutedfrom the column with hexane. The amount of such eluted polymer isdetermined gravimetrically to obtain the weight percent of polybutenereacted with MA. The total tarry product produced is weighed and itsweight percent of total charge (polymer plus MA) is calculated. Theresults of said five examples, of which two are control (no additive)are shown in Table I below.

                  TABLE I                                                         ______________________________________                                        EFFECT OF DRY HYDROGEN CHLORIDE ON POLYBUTENE-MA REACTION                     Example  Additive                                                             Number   Name       Conc., ppm                                                                              Yield, %                                                                              Tar,%                                   ______________________________________                                        1        None        0        66.0    1.5                                     2        None        0        66.4    1.1                                     3        Dry HCl     93       69.9    0.3                                     4        Dry HCl    128       70.1    0.1                                     5        Dry HCl    360       70.2    0.2                                     ______________________________________                                    

The next five examples were conducted with a second sample polybutene of957 M_(n) containing 21 ppm total chlorine (from polymerization). Aswill be noted additives differing from those used in Examples 3-5 areused in the following examples. Such three additional examples wereotherwise conducted as before described with respect to the previousexamples but at 249°C. The results of those five examples are shown inTable II below.

                  TABLE II                                                        ______________________________________                                        EFFECT OF HALOGEN-CONTAINING ADDITIVES                                        ON POLYBUTENE-MA REACTION                                                     Example                                                                              Additive                                                               Number  Name          Conc., ppm                                                                              Yield, %                                                                             Tar, %                                 ______________________________________                                        6      None            0        63.3   1.3                                    7      Iodine          75       68.0   0.9                                    8      Iodine Mono-    72       71.8   0.3                                           chloride                                                               9      Calcium Bromide (1)                                                                          100       70.0   0.8                                    10     Calcium Bromide (2)                                                                          100       70.6   0.2                                    ______________________________________                                         (1)Additive was pre-suspended in polybutene.                                  .sup.(2) Additive was charged directly to reactor.                       

The following two examples were conducted on a larger scale using anautoclave having a motor driven dual impeller, automatic heat control,pressure gauge and means for sampling reaction product before itsdischarge from the autoclave. After completion of the reaction, excessmaleic anhydride was stripped off, the product was filtered and thefiltrate analyzed for yield. Unreacted polybutene was determined asbefore described. The polybutenylsuccinic anhydride % yield is on astoichiometric basis. Filter cake tar and reactor retained tar arecollected and the total reported as "Weight % Tar."

                  TABLE III                                                       ______________________________________                                        EFFECT OF INORGANIC HALIDES ON                                                POLYBUTENE-MALEIC ANHYDRIDE REACTION                                          Example Additive           Adduct    Tar                                      Number  Name        Conc., ppm Yield, %                                                                              Wt. %                                  ______________________________________                                        11      None         0         65.2    0.84                                   12      Iodine                                                                         Monochloride                                                                             60         68.0    1.20                                   ______________________________________                                    

Examples 9 and 10 used 957 M_(n) polybutene and 11 and 12 used 911 M_(n)polybutene.

While the foregoing examples illustrate benefits afforded by presentinventive polybutene compositions containing viscous polybutenes havingM_(n) of 900-950, the use of other viscous polybutenes in the M_(n)range of about 300 to 3,000 will provide polybutene compositionsaffording yield improvement and tarry material suppression in the mannerand nature above illustrated for the maleic anhydride reactionsillustrated. Similar benefits can be expected by the use of the presentinventive polybutene compositions with other of the before namedunsaturated anhydrides of aliphatic dicarboxylic acids. Furthermore, theuse of the inventive inorganic halide additives can be extended toreaction of unsaturated anhydrides with other olefin compositions (e.g.,polypropenes).

Finally, the inorganic halide additives are equally useful whether theyare added to the olefin polymer, the unsaturated anhydride or mixturesthereof.

What is claimed is:
 1. In the reaction between 300-3,000 M_(n) butenepolymer and maleic anhydride to prepare polybutenyl-substituted succinicanhydride, the improvement comprising conducting said reaction at atemperature of from 150° to 300°C in the presence of 5-200 ppm based onsaid polymer of dry hydrogen chloride or calcium bromide.
 2. The methodof claim 1 wherein the inorganic halide is dry hydrogen chloride.
 3. Themethod of claim 1 wherein the inorganic halide is calcium bromide.